This invention relates to a plating activator for electrolytic nickel plating (hereinafter designated as electro-nickel plating) on a ceramic body, and more particularly, pertains to such an activator containing a high percentage of silver.
The activation of a nonconductive surface for electroless plating nickel has traditionally been accomplished by depositing a thin layer of palladium, e.g. as described in U.S. Pat. No. 2,690,402 issued Sept. 28, 1954. Improvement in the quality and adherence of nickel plating on a ceramic body was achieved by the addition to palladium in the activator of silicon and zinc in the patent to John P. Maher, U.S. Pat. No. 4,425,378 issued Jan. 10, 1984 and assigned to the same assignee as the present invention. In one limiting example (Example 22) of the Maher patent the palladium makes up a little more than 5 weight percent of these ingredients and at the other end of the workable spectrum (Example 13) palladium amounts to 37 percent of these three ingredients.
The substantial quantities of palladium used in such activators makes the expense of the activator a significant percentage of the total cost of electroless plating.
Silver has been used as a thin activator layer on a ceramic body deposited in preparation for plating copper, and then silver, e.g. for use as a mirror. However, the adherence of a nickel plate over a silver activator is inadequate for terminals on a ceramic chip component which terminals are not only the means by which electrical access is had to the component but are also the means by which the component is physically mounted.
Nickel electro-plating of a ceramic body is also accomplished by first applying a coating of a paste containing silver powder and an acid resistant glass frit, and firing this coating. Such cermet pastes are applied relatively thickly, contain a great deal of silver per square area covered, and are not entirely conformal with the ceramic body so that overall dimensions are difficult to control. Of course, other relatively noble metals, such as palladium, could be substituted for the silver in an electro-plating activator composition but with no known advantage; the cost of palladium being more than 50 times greater than that of silver, such substitution has been contraindicated.
It is an object of the present invention to provide an improved electro-nickel plating activator composition capable of being effective as a thin film in the preparation for the electro-plating of nickel on a ceramic body that provides high plating quality and strong adherence while having a low cost.